Healthy kidneys function to retain the correct amount or volume of fluid in the body. For a patient with chronic kidney disease, the fluid volume in the body fluctuates between overhydration and underhydration due to the inability of the kidneys to properly regulate the amount of fluid in the body. Many patients with chronic kidney disease are treated with concomitant fluid or volume overload therapies such as renal replacement therapy (RRT), pharmacological therapy (e.g. diuretic), ultrafiltration and neurotherapy. Examples of RRT include dialysis, hemofiltration, hemodiafiltration, ultrafiltration, etc., which aid in regulating the fluid volume in the patient. In many RRTs, fluid removal goals are adjusted based on the difference between the weight of the patient at the beginning of the RRT and his/her “dry weight” or “normal hydration state”. However, traditional methods used to determine the dry weight or the normal hydration state of a patient, such as body weight, blood pressure, and clinical status, can be inaccurate. Because patients with renal disease often experience weight loss as a part of the renal disease state, the dry weight of a patient is often overestimated, causing the patient to become overhydrated while on RRT. Overhydration can have severe cardiovascular effects such as hypertension, right heart failure, pulmonary edema and left ventricular hypertrophy. In a patient whose dry weight is underestimated, intradialytic hypotension is a common and difficult clinical management problem. There is a continuing need for improved measurement of the fluid status of a patient that can be chronically obtained before, during and after a RRT in a minimally invasive manner.